The art of screen printing utilizes a tensioned screen or mesh mounted on a frame having a stenciled image thereon. Ink is applied through the screen in the areas where the stencil has not blocked the openings between the threads of the mesh. The screen is typically fixed onto a rectangular (sometimes square) frame. The present invention particularly relates to a roller frame which includes a plurality of rollers coupled together by corners. The corner members support the rollers for rotation about their longitudinal axes. Each roller includes a longitudinally extending channel or other screen securing means on its periphery so as to retain an edge portion of the screen during tensioning. The rollers are locked to the corner members at a rotated position so that the desired tension is maintained within the screen.
The typical screen printing roller frame includes a series of extruded hollow aluminum tubes. An end plug is secured or welded onto the end of the tube. The end plug is typically integrally formed with a nut-like structure which forms the rotation means for the roller. The corner of the frame is attached to the roller, outside of the end plug and its corresponding rotational nut.
The manual method of stretching a screen on a roller frame uses a wrench or the like which is applied to the nut-like portion of the end plug. As the wrench rotates the roller, the screen is tensioned. A bolt threaded into the end of the roller is used to secure the roller to the corner member at the desired rotated position, thus fixing the tension in the screen.
U.S. Pat. No. 5,488,901 to Jerome J. Hruska, which is herein incorporated by reference, shows a device for substantially automatically stretching a screen on a roller frame. The device includes a series of torsion stations located at each corner of the frame. Each torsion station includes a torsion tool which is attached to a shaft structure at a first pivot point. Each torsion station also has a support to which the shaft structure is attached at a second pivot point. The length of each shaft between the first and second pivot points is variable for the purpose of rotating the respective torsion tools and corresponding roller on the frame. A wrench head included in the torsion tool engages one end of each roller. Each of the shafts include a pneumatically powered cylinder positioned between the first and second pivot points. The pneumatic cylinders vary the length of the shaft, thereby causing the torsion tool to rotate and torque the attached roller. The present invention relates to an improvement to the device shown in Hruska U.S. Pat. No. 5,488,901.